The effect of equal-channel angular pressing (ECAP) on the structure-phase state and superplasticity development was investigated using the 1421 Al-Mg-Li alloy. The physical reasons for the displacement of the temperature range of superplasticity to lower temperatures after ECAP by comparison with the initial state are considered. Possible reasons are discussed for the decrease in the activation energy of true grain boundary sliding in the alloy produced using ECAP by comparison with the initial condition.